The present invention relates to a hydrodynamic bearing for a motor and the motor having the same, which is used for a data processing apparatus such as a data storing apparatus having a disk drive, or a printer, or, for an entertainment apparatus having a disk drive for recording or reproducing images or sounds, or the like.
In recent years, under the circumstance that the reduction of size and weight, high density recording, high speed data processing and the like are required in a data processing apparatus or in an entertainment apparatus, the improvement of the performance of a motor (small spindle motor in this occasion) used for the apparatus is also required.
In regard to the improvement of the performance of the motor, the reduction of the rotational runout of the rotor of the motor, the reduction of the noise and the improvement on the durability of the motor are mostly required, for which the improvement of the performance of a bearing used for the motor is also required.
The runout of the rotor and the noise of the motor are caused by the magnetic attraction and repulsion between the rotor magnet and the stator of the motor. That is, the rotating shaft of the rotor radially vibrates and bumps against the bearing of the rotor when the rotor is rotated. A conventional motor having a bearing whose bearing is made of sintered oleo-metal can hardly reduce the runout and the noise of the motor to a sufficiently low level.
For the improvement on the above problems, a hydrodynamic bearing has been developed, and the bearing is now being put into practical use. The hydrodynamic bearing comprises, which denotes the dimension from the turning point 163 to the end thereof in the second side. That is, the second herringbone pattern 157 is asymmetrical.
An oil reserving groove 159 is formed on the inner wall of the sleeve 155. The oil reserving groove 159 is located at the position which corresponds to the intermediate portion between the first herringbone pattern 156 and the second herringbone pattern 157 of the rotating shaft 154. A through-hole 160 is formed through the wall of the sleeve 155 in such a manner that the through-hole 160 radially extends from the oil reserving groove 159 to the outside of the sleeve 155.
In the above conventional structure, the dynamic pressure of the oil 161, which is generated at the herringbone pattern 157 when the shaft 154 is rotated, forms a stream of the oil 161, which flows toward the second side (i.e., the side where the shaft end 162 is located) since the width-E is larger than the width-F, which causes the occurrence of air bubbles in the oil 161 since air comes into the space in the sleeve 155 from the through-hole 160. Then the air bubbles further push the oil 161 outward from the space in the sleeve 155, which result in the shortage of oil 161 and causes the increase of the runout of the shaft 154 and the damage on the durability of the motor having the bearing.
FIG. 16 is a partially schematic sectional view showing another example of the structure of the hydrodynamic bearing. This type of bearing, which is also known in general, is disclosed in Japanese Utility Model Publication No.2560501.
In FIG. 16, a rotating shaft 164 is rotatably supported by a sleeve 165. A thrust bearing plate 168 is fixed to the sleeve 165 and supports one end of the shaft 164. Oil 169 is filled in the space formed with the sleeve 165, the rotating shaft 164 and the thrust bearing plate 168. On the outer wall of the rotating shaft 164, a first herringbone pattern 167 and a second herringbone pattern 166 are formed. The first herringbone pattern 167 is located at a first side (i.e., the side where the thrust bearing plate 168 is located). The second herringbone pattern 166 is located at a second side (i.e., the side opposite the first side). for example, a cylindrical rotating shaft and a sleeve, and, a fluid (oil, in most cases) is filled in a space formed with the sleeve and the rotating shaft which is inserted into the sleeve. A herringbone pattern is formed either on the shaft or on the sleeve. In the above structure, when the rotor is rotated, the rotating shaft is supported by the dynamic pressure of the fluid, which is generated at the herringbone pattern.
The hydrodynamic bearing has advantages that the size of the bearing can be reduced since the mechanical components and portions of the bearing share relatively small space comparing with that in the other bearings. Also, since the rotating shaft is supported by the sleeve via the fluid, the noise of the motor can be reduced, and the motor having the bearing is durable against shock. Also, since the load on the rotating shaft is supported by the whole circumference of the shaft (which generates an integral effect), the runout of the shaft is reduced. As is described above, the hydrodynamic bearing is structurally superior for the spindle motor.
In the hydrodynamic bearing, the structure disclosed in Japanese Non-Examined Patent Publication H6-137320 is known in general. The structure disclosed in the publication is described hereinafter with reference to FIG. 15 which is a partially schematic sectional view showing the structure of the bearing.
In FIG. 15, a rotating shaft 154 is rotatably supported by a sleeve 155. A thrust bearing plate 158, which is fixed to the sleeve 155, supports one end of the shaft 154. Oil 161 is filled in the space formed with the sleeve 155, the shaft 154 and the thrust bearing plate 158. On the outer wall of the shaft 154, a first herringbone pattern 156 and a second herringbone pattern 157 are formed. The first herringbone pattern 156 is located at a first side (i.e., at the side where the thrust bearing plate 158 is located). The second herringbone pattern 157 is located at a second side (i.e., the side opposite the first side).
In the second herringbone pattern 157, width-E, which denotes the dimension from the turning point 163 of the pattern 157 to the end thereof in the first side, is larger than width-F
In the second herringbone pattern 166, width-G, which denotes the dimension from the turning point of the pattern 166 to the end thereof in the second side, is larger than width-H which denotes the dimension from the turning point of the pattern 166 to the end thereof in the first side.
Also, in the first herringbone pattern 167, width-I, which denotes the dimension from the turning point of the pattern 167 to the end thereof in the second side, is larger than width-J which denotes the dimension from the turning point of the pattern 167 to the end thereof in the first side. That is, both patterns 166 and 167 are respectively asymmetrical.
Also, two through-holes 170 and 171 are formed through the thrust bearing plate 168.
In the above structure, the oil 169 flows outside from both through-holes 170 and 171, such that the oil 169 has to be refilled for the continuous operation of the motor having this type of bearing. That is, the bearing is not suitable for continuous long time operation.
When the through-holes 170 and 171 are closed for preventing the leakage of the oil 169, the pressure around the thrust bearing plate 168 becomes high and air bubbles occur there, such that the shaft 164 enters into a state of unstable floating relative to the thrust bearing plate 168, which results in a serious problem, for instance, that the disk of a disk drive touches the pickup head of the disk drive when such a bearing is used for the spindle motor of the disk drive, due to the axial runout of the rotating shaft.
The object of the present invention is to address the problems in the conventional hydrodynamic bearing and to provide a durable hydrodynamic bearing in which the uniform and stable thickness of the oil film for the hydrodynamic bearing is realized for reducing both radial and axial runout of the rotating shaft. Another object of the present invention is to provide a motor having the durable bearing and a disk drive having the motor.
For realizing the above object, the bearing of the present invention comprises:
(a) a rotating shaft,
(b) a sleeve which surrounds the outer wall of the rotating shaft and supports the rotating shaft in such a manner that the shaft is rotatable, and
(c) a thrust bearing plate which is fixed to the sleeve and supports one end of the rotating shaft,
where in a first herringbone pattern and a second herringbone pattern are formed either on the rotating shaft or on the sleeve, wherein the first herringbone pattern is located at a first side and the second herringbone pattern is located at a second side, wherein the first side is the side where the thrust bearing plate is located, and the second side is the side opposite the first side,
wherein the relation between width-A and width-B in the first herringbone pattern is expressed by
0 less than (Axe2x88x92B) less than 0.2x(A+B)
where A denotes the dimension from the turning point of the first herringbone pattern to the end thereof in the first side, and B denotes the dimension from the turning point to the end thereof in the second side, and, the relation between width-C and width-D in the second herringbone pattern is expressed by
0 less than (Dxe2x88x92C) less than 0.2x(D+C)
where C denotes the dimension from the turning point of the second herringbone pattern to the end thereof in the first side, and D denotes the dimension from the turning point to the end thereof in the second side.
The above structure enables the improvement of both durability and stiffness of the bearing.
Also, another structure of the bearing for realizing the above object comprises:
(a) a rotating shaft,
(b) a sleeve which surrounds the outer wall of the rotating shaft and supports the rotating shaft in such a manner that the shaft is rotatable, and
(c) a thrust bearing plate which is fixed to the sleeve and supports one end of the rotating shaft,
wherein a first herringbone pattern and a second herringbone pattern are formed either on the rotating shaft or on the sleeve, and an oil reserving groove is formed on the sleeve, wherein the oil reserving groove is located at the position which corresponds to the intermediate portion between the first herringbone pattern and the second herringbone pattern, and a through-hole and an air-bubble-holding-hollow are formed in the wall of the sleeve, wherein the through-hole extends from the thrust bearing plate up to the oil reserving groove, also up to the air-bubble-holding-hollow.
In the above structure, since oil can be reserved in the through-hole too, the shortage of the oil is more surely prevented, and also, air bubbles in the bearing can be more surely eliminated, such that the further improvement of the durability of the bearing can be realized.
Also, still another structure of the bearing for realizing the above object comprises:
(a) a rotating shaft,
(b) a sleeve which surrounds the outer wall of the rotating shaft and supports the rotating shaft in such a manner that the shaft is rotatable, and
(c) a thrust bearing plate which is fixed to the sleeve and supports one end of the rotating shaft,
wherein a first herringbone pattern and a second herringbone pattern are formed either on the rotating shaft or on the sleeve, wherein the turning point of the first herringbone pattern and the turning point of the second herringbone pattern are located on a same phantom line axially extended on the surface of the rotating shaft.
In the above structure, the phase of dynamic pressure (i.e., the operating phase of the stiffness of the bearing) at the first herringbone pattern agrees with that at the second herringbone pattern, such that the runout including Non-Repeatable Runout (NRRO) of the rotating shaft can be reduced.
Also, for realizing the above object, the motor of the present invention comprises:
(a) a rotor having a rotating shaft fixed thereto,
(b) a bearing, and
(c) a stator having the bearing,
wherein the bearing used for the motor is one of the above bearings.
The above structure enables the motor to have advantages of the bearing described above.
Also, for realizing the above object, the disk drive of the present invention has a motor comprising:
(a) a rotor which has a rotating shaft fixed thereto and rotates a disk,
(b) a bearing, and
(c) a stator having the bearing,
wherein the bearing used for the motor is one of the above bearings.
The above structure enables the disk drive to have advantages of the bearing described above.